20.5: Gene Expression and Cancer

Question 1

What is cancer

Answer 1

Cancer is a group of diseases caused by damage to the genes that regulate mitosis. This causes unrestrained growth of cells

Question 2

What is a tumour

Answer 2

A tumour is uncontrollable growth of cells that constantly expands

Question 3

Two types of tumours

Answer 3

1. Benign (being, doesnt really do anything)

2. Malignant (bookey)

Question 4

Benign Tumour vs Malignant tumour

Answer 4

Benign

• Large
• Grow slow
• Light, normal nucleus
• Specialised
• Produce adhesion molecules and dont move
• Stay in a capsule (no finger-like projections)

Malignant

• Large
• Grow fast
• Dense, dark nucleus due to lots of DNA
• Unspecialised
• Don’t produce adhesion molecules and can move around
• Grow finger-like projections that enter other cells

Question 5

How does cancer formation begin

Answer 5

Cancer cells are derived from one single mutant cell that is constantly dividng

Question 6

What two genes play a part in cancer

Answer 6

1. Tumour Suppressor Gene

2. Oncogenes

Question 7

What is an oncogene

Answer 7

Most oncogenes are mutations of proto-oncogenes that have been switched on permanently

Question 8

What are proto-oncogoenes

Answer 8

Proto-oncogenes stimulate a cell to divide when growth factors attach to protein receptors on its cell membrane

This activates genes that cause DNA to replicate and the cell to divide

If a proto-oncogene mutates into an oncogene it may be permanently switched on

Question 9

Why can a proto-oncogene be permanently switched on

Answer 9

1. The receptor protein on the cell-surface membrane can become permanently activated, so cell division constantly occurs
2. The oncogene may code for a growth factor that is produced excessively

Question 10

Result of oncogene formation

Answer 10

1. Cells divide too rapidly and out-of-control

2. Development of tumours

Question 11

Can proto-oncogenes be inherited

Answer 11

Yes, they can be inherited leading to a greater risk of tumour formation

Question 12

What is a tumour-suppressor gene

Answer 12

Tumour-suppressor genes slow-down cell division, repair mistakes and tell cells when to die (apoptosis)

Question 13

Role of tumour-suppressor genes

Answer 13

A normal tumour suppressor gene maintains normal rates of cell division and prevents the formation of a tumour

Question 14

What can occur if a tumour-suppressor gene becomes mutated

Answer 14

The tumour-suppressor gene may become permanently switched off. This results in the failure to inhibit cell growth and cells can grow out of control and form tumours

Question 15

Typical mutations of tumour-suppressor genes

Answer 15

Hypermethylation - increased methylation

Question 16

Process of hypermethylation

Answer 16

1. Hypermethylation occurs in the promoter region of a tumour suppressor gene
2. this leads to the tumour suppressor gene becoming inactivated
3. As a result, transcription of promoter regions of tumour suppressor genes is inhibited
4. As a result, the TSG is silenced
5. As the TSG usually slows down the rate of cell division, its deactivation leads to increased cell division and the formation of a tumour

Question 17

Oestrogen production and breast cancer

Answer 17

Following menopause, the fat cells in breasts produce more oestrogen.

Once a tumour has developed, it further increases oestrogen concentration which leads to increased development of the tumour. This leads to even greater development of the tumour